| With the urgent need for rapid development of industry and requirement for environmental protection, the operation temperature of high efficiency energy conversion systems (such as gas turbine, etc.) is much higher, due to the large number of applications of natural gas, the gas turbine always work in environment of water vapor as well as the content is increase quickly. On the other hand the gas turbine which operated in the marine environment, affected by the marine atmosphere seriously in ship engines. Currently, the application of protective coating on the surface of high temperature alloy has become an effective way to solve the problem of high temperature oxidation corrosion of hot components in high temperature and harsh environment, meanwhile it play a key role in the technical field of aviation, military, and national defense. As one of the hottest heat protective coating, thermal barrier coating due to the effect of internal stress easy to generate the crack in the ceramic layer and peeling off in high temperature and complex environment. Therefore, the preparation of the coating with a new structure, which can generate in situ a lot of ceramic insulating layer during the process of high temperature service, thereby slowing flake coating cracking, at the same time has good high temperature oxidation resistance.Si-modified aluminized coating has been proved to have excellent high temperature oxidation corrosion resistance. In order to prepare the AISi coatings which have porous outer layer and inner density structure, we use the hot dip aluminum technology and vacuum diffusion treatment process on nickel-based alloy K438 surface in this article. Analysis the formation mechanism and oxidation behavior of AISi coating with porous structure in the static air, water vapor and salt atmosphere at 1050℃. Electronic balance, energy dispersive spectrometer (EDS), Scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA) used to analyze oxidation kinetics, phase composition, surface morphology different oxidation time, the cross-sectional shape and tissue composition of the alumina-silica coatings. The main results as follows:(1) Prepared the coatings on the surface of nickel base alloy have a double-layer structure contain a porous layer and a diffusion layer, due to pores in the porous layer, we found that can reduce the thermal conductivity obviously of the coatings.(2) In the process of high temperature oxidation, the porous layer and the alloy surface formed the alumina ceramic in situ place rapidly, thereby significantly enhancing the heat insulation performance and oxidation resistance.(3) In static air the diffusion region of porous AISi coating contain large amounts of β-(Ni,Co)Al phase which act as Al-storage, during the oxidation process, it can continue to provide al source to support the alumina layer growth and repair, thus improve the performance of the resistance in high temperature oxidation.(4) Oxidation in high temperature with water vapor, the water vapor can promote the steady state α-Al2O3 generation, the surface of the coating formed a continuous and dense α-Al2O3 scale,which will show a better oxidation resistance than that in static air.(5) Porous alumina-silica coatings oxide in salt atmosphere, in the late oxide state, the oxide layer thickening on the surface of the coating constantly generate large stress and corrosive gas corrosion led to the oxide layer peeling phenomenon, began to develop in the direction of failure of the coating.
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